Low reflection of light from an external light source such as a fluorescent lamp is required of the display surface of image display devices such as liquid crystal displays (LCDs), cathode-ray tube display devices (CRTs) and the like from the viewpoint of enhancing the visibility.
It has hitherto been known that covering the surface of a transparent object with a transparent film having a low refractive index reduces the reflectance. The visibility can be improved by providing an antireflective film utilizing this phenomenon on the display surface of an image display device. The layer construction of the antireflective film is provided by forming a high-refractive index layer or a medium-refractive index layer on a surface which should prevent reflection, and further forming a low-refractive index layer on the high-refractive index layer or the medium-refractive index layer.
Methods for the formation of the high-refractive index layer or medium-refractive index layer in the antireflective film are generally classified roughly into gas phase methods and coating methods. Gas phase methods include physical methods such as vacuum deposition and sputtering and chemical methods such as CVD. Coating methods include roll coating, gravure coating, slide coating, spray coating, dip coating, and screen printing.
The gas phase method can form thin-film high-refractive index layer and medium-refractive index layer having high function and high quality, but on the other hand, the gas phase method is disadvantageous in that close control of atmosphere in a high vacuum system is necessary and, at the same time, a special heating device or an ion generation accelerator is necessary and, consequently, a complicated and increased-size production apparatus is necessary, necessarily leading to increased production cost. Further, the formation of a large-area thin film as the high-refractive index layer and medium-refractive index layer or the formation of a thin film having even thickness on the surface of films or the like having a complicated shape is difficult.
On the other hand, among the coating methods, the spray method is disadvantageous, for example, in that the utilization efficiency of the coating liquid is poor and the control of film formation conditions is difficult. Roll coating, gravure coating, slide coating, dip coating, screen printing and the like have good utilization efficiency of the film forming material and are advantageous in terms of mass production and equipment cost. In general, however, the high-refractive index layer and medium-refractive index layer formed by the coating method are disadvantageously inferior to those formed by the gas phase method in function and quality.
A method comprising coating a coating liquid comprising high-refractive index fine particles of titanium oxide, tin oxide or the like dispersed in a solution of a binder of an organic material onto a substrate to from a coating film has recently been proposed as a coating method that can form thin-film high-refractive index layer and medium-refractive index layer having excellent quality.
Patent document 1 describes that, in the formation of a coating film having a low refractive index, a coating composition containing rutile-type titanium oxide treated with an inorganic compound is excellent in dispersibility, dispersion stability, and evenness of coating and can easily form an even large-area thin film. The coating film formed using the coating composition described in patent document 1, however, had unsatisfactory lightfastness.
Patent document 2 discloses that a coating composition containing a rutile-type titanium oxide treated with an inorganic compound is used for providing an antireflective film suitable for mass production. The coating film formed using the coating composition disclosed in patent document 2, however, had unsatisfactory lightfastness.
Patent document 3 discloses that, in order to form an antireflective coating film having improved lightfastness, a metal oxide treated with a zinc chelate compound is incorporated in the coating composition. Even for the coating film formed using the coating composition disclosed in patent document 3, the lightfastness was still unsatisfactory.    [Patent document 1] Japanese Patent Laid-Open No. 275430/2002    [Patent document 2] Japanese Patent Laid-Open No. 166104/2001    [Patent document 3] Japanese Patent Laid-Open No. 371236/2002